he must try all. KOH is also a good option for sure. KOH, DRIE or HF+HNO3+wafer...the one which works best. --- On Mon, 8/17/09, Xiaoguang Liuwrote: From: Xiaoguang Liu Subject: Re: [mems-talk] KOH etch To: "General MEMS discussion" Date: Monday, August 17, 2009, 3:43 PM I don't think DRIE will give the same smoothness as an KOH etch. For renil's purpose, I think any concentration between 15%-50% will work, because <111> surface is usually quite smooth over a wide range of KOH concentrations. Best Leo